Two main requirements are posed to an elevator rope: safety and service life. The requirements for elevator ropes are described in European Norm EN 81-1:1998+AC:1999, the more relevant parts being 9.1, 9.2 and 9.3, and annexes M and N.
Safety is ensured by inspection (visual and on regular time intervals), redundancy (at least two ropes carry the cart) and the safety factor (called SF hereafter, i.e. the ratio of breaking load of the rope to the maximum load of cart and freight), which has to be above a certain number (e.g. 12 when 3 ropes are used).
Service life is maximised by the design of the sheave and the rope.
First there is the importance of the metal-to-metal contact on the sheave:                Hard, higher tensile wires lead to excessive wears of sheave and rope so only lower tensile wires can be used.        The pressure of the wires on the sheave has to be low enough leading to a requirement of a relatively thick rope.        
Second there is the rope design:                Small lay lengths of the cable strands result in an increased service life.        Parallel lay is used resulting in line contacts between the wires, such line contacts leading to less cutting between the wires, hence resulting in a longer service life.        A minimum sheave diameter of 40 times the rope diameter results in low bending stresses in the wire, hence again improving the service life of the rope.        Impregnating the textile core with lubricant increases the service life.        
These requirements have led to elevator ropes as they are known in the art. I.e. wire ropes with a core of a lubricated textile material (e.g. sisal) surrounded by typically 8 strands assembled out of bare or galvanised steel wires having a tensile strength of between 1200 up to 2050 N/mm2. The strands themselves typically contain between 19 and 36 wires and are of parallel lay type as e.g. Warrington, Seale, filler or a combination type e.g. Warrington-Seale. The lay length of the strand in the rope is typically between 5 to 6 times the diameter of the rope. The size of the rope is chosen in function of the total mass of the elevator cart and its load. The diameter range is from 6 to 22 mm, while sizes between 8 to 11 mm are most popular. The international standard ISO 4344 describes these ropes in general.
Although the prior art ropes have fulfilled the requirements for more than a hundred years, they have some inherent drawbacks. First the requirement for a relatively thick rope, in order to reduce rope pressure on the traction sheave, combined with the requirement that the traction and diverting sheave diameters must be at least 40 times the diameter of the rope leads to large sheaves and consequently large machine space requirements. Secondly the relatively small cable lay with respect to the diameter of the rope results in a low modulus or a high elastic elongation leading to a load dependent position of the cart with respect to the floor level. Thirdly the textile core leads to creep which necessitates the regular adjustment of the rope length certainly in the initial stages of the rope usage. A fourth drawback is that the lubricated core regularly needs re-lubrication that can be done manually or by means of an automated lubricant applicator. In either case the cost of the system increases. Also the re-lubrication can considerably change the traction of the rope to the drive pulley, leading to an uncontrolled coefficient of fiction between sheave and rope.
Recent solutions to overcome these problems have been suggested in EP 1 213 250 A1. In this application, an elevator is claimed using an elevator rope having small sized, high tensile wires and an elastomeric coating either inside or outside the rope. While this arrangement will indeed eliminate the first drawback of a relatively large sheave and consequently a large machine space requirement, it does not address the second drawback on the plastic elongation of the rope and the third drawback on the creep phenomenon. In addition, it does not address the problem of how to preserve the integrity of the rope, since it is composed of totally different materials. Hence no indication is given on how to maintain or improve the service life of the rope vis-à-vis the currently used wire ropes which presents a new, fifth drawback